(1) Field of the Invention
This invention relates to a deposition process, and more specifically to a deposition process making use of a plasma so that a photoreactive gas is caused to undergo a reaction by light radiated from the plasma and the reaction product is deposited on a substrate.
(2) Description of the Prior Art
A variety of research has been carried out and is still under way to form amorphous silicon films having relatively large areas by deposition processes which films are useful as materials for fabrication of photosensitive drums in electrostatic photocopiers and solar batteries. Besides, it has also been investigated to form insulative films and protective films by the deposition process, as disclosed for example in Japanese Patent Laid-open No. 163,792/1979. As led by the above researches and investigations, a variety of deposition processes has been proposed.
The present invention relates especially to a chemical decomposition deposition process making use of a photochemical reaction, which process is a sort of deposition process. The chemical decomposition deposition process has such merits that its film-forming velocity is very high and a deposition over a large area can be effected advantageously. Owing to these merits, the chemical decomposition deposition process has recently attracted special attention.
The conventional chemical deposition process making use of a photochemical reaction comprises, as disclosed in the aforementioned specification, disposing a substrate for deposition in a vessel made of a material which permits transmission of ultraviolet rays with a high efficiency, feeding a photoreactive gas into the vessel and causing the photoreactive gas to flow through the vessel, irradiating ultraviolet rays externally from a u.v. discharge lamp onto the substrate to cause the photoreactive gas to undergo a photochemical reaction and allowing the reaction product of the photochemical reaction to deposit on the substrate. Although the chemical decomposition deposition process has, as mentioned above, such merits that its film-forming velocity is high and it may be applied to large substrates, it has been found to involve such drawbacks that the reaction product is also allowed to deposit possibly on the inner wall of the vessel and the transmission of ultraviolet rays is thus impaired to a considerable extent.
It is difficult to wash the inner wall of the vessel frequently in an actual film deposition work. With a view toward overcoming this problem, some special vessels and reactors have been proposed. However, they are complex in structure and difficult in handling.